1. Field of the Invention
The present invention relates to an optical wavelength switch having a planar lightwave circuit structure for use in optical communication, etc.
2. Description of the Related Arts
In recent years, communication capacity has explosively increased and construction of a photonic network having a large capacity using Wavelength Division Multiplexing (WDM) for coping with the increase has made progress. For an efficient composition of the WDM photonic network, wavelength switches are indispensable which realize Optic Add-Drop Modules (OAD) or optical cross-connect modules disposed in optical transmission paths.
FIG. 1 is a diagram illustrating an optical add-drop module 10 and this module 10 inputs an input optical beam having been wavelength-multiplexed from a previous-stage node into an input port 11 and inputs an insert (Add) optical beam having a specific wavelength at the node into an insert port 12. Furthermore, a part of the input optical beam 11 and the insertion optical beam 12 are outputted unprocessed passing through (Through) to an output-side port 13 and a part of the input optical beam 11 having a specific wavelength is branched (Drop) to a branch port 14.
The functions of insertion (Add), passing through (Through) and branching (Drop) of an optical signal at the optical add-drop module 10 are realized by a wavelength switch. For a conventional wavelength switch having such functions, a composition as shown in FIG. 2 is known (see U.S. Pat. No. 5,960,133).
A composition shown in FIG. 2 comprises a combination of a diffraction grating (spectral function) 101, a MEMS (Micro-Electro Mechanical System) mirror 102 having a switching function and a focus lens 103.
The input optical beam (IN) and the insertion optical beam (ADD) are divided by the diffraction granting 101 into optical beams for each wavelength and inputted into the MEMS mirror 102 through the focus lens 103. At the MEMS mirror 102, it is possible to switch an optical beam to either an output (OUT) port or a branch (DROP) port by controlling the angle of the mirror.
Here, in order to downsize a WDM transmission system and reduce the cost on it, it is desired to realize the functions of the optical add-drop module 10 described referring to FIG. 1 using planar lightwave circuit (PLC) type functional integrated circuits capable of being mass-produced using a batch process.
However, for a combination of a diffraction grating 101 and an MEMS mirror 102 having a composition of a conventional example shown in FIG. 2, a high-precision alignment is necessary for the focus lens 103 and the MEMS mirror 102 in order to focus optical beam emitted from the diffraction grating 101, on the MEMS mirror 102.
To this end, there are problems that the number of assembly steps becomes great many and that cost reduction is difficult. Furthermore, it is very difficult to downsize and reduce the thickness of the switch because optical beams are propagated in a three (3)-dimensional space.